Electric instantaneous water heater

ABSTRACT

An instaneous water heater includes a main electrically insulating body having an inlet and an outlet. A flow duct means extends between the inlet and outlet and includes an inlet bore, an outlet bore, a heater bore means, a first flexible, electrically insulating tube extending between the inlet bore and the heater bore means and a second flexible, electrically insulating tube extending between the heater bore means and the outlet bore. The inlet bore, outlet bore and the heater bore means are formed in the main body while the first and second tubes are formed separately and independently of the main body and each other. A clamping plate connects the ends of the tubes with respect to inlet bore, outlet bore and heater bore means. The tubes together with the inlet and outlet boers define a length sufficient to provide a resistance path which minimizes leakage current flow from an electric heater disposed within the heater bore means. A flow responsive switch means controls current flow the electric heater. A thermostat may be provided in series with the flow responsive switch.

United States Patent [1 1 Gardom 1 ELECTRIC INSTANTANEOUS WATER HEATER [75] Inventor: George William Gardom, Sutton Coldfield, England [73] Assignee: Gardom & Lock Limited, West Bromwich, Staffordshire, England [22] Filed: Dec. 6, 1971 [21] Appl. No.: 205,232

[52] US. Cl 219/309, ZOO/81.9, 219/307, 219/328, 219/332, 219/496 [51] Int. Cl H051) l/0 2, F24h H10 [58] Field of Search .219/296-309r 332, 496; 200/819 [56] References Cited UNITED STATES PATENTS 793,1 18 6/1905 Wright 219/299 X 1,534,298 4/1925 Clark 219/299 1,799,626 4/1931 Keith 219/302 UX 2,400,618 5/1946 Wicks 219/307 UX 3,531,622 9/1970 Kaiser 219/309 2,471,133 5/1949 Wicks 219/307 2,588,314 3/1952 Wicks 219/309 FOREIGN PATENTS OR APPLICATIONS 1,112,621 8/1961 Germany 219/296 1,062,522 3/1967 Great Britain 219/307 1,235,849 6/1971 Great Britain 219/307 221,542 11/1942 Switzerland 219/309 Dec. 25, 1973 Primary Examiner-A. Bartis Attorney-Neil F. Markva et a1.

[57] ABSTRACT An instaneous water heater includes a main electrically insulating body having an inlet and an outlet. A flow duct means extends between the inlet and outlet and includes an inlet bore, an outlet bore, a heater bore means, a first flexible, electrically insulating tube extending between the inlet bore and the heater bore means and a second flexible, electrically insulating tube extending between the heater bore means and the outlet bore. The inlet bore, outlet bore and the heater bore means are formed in the main body while the first and secondtubes are formed separately and independently of the main body and each other. A clamping plate connects the ends of the tubes with respect to inlet bore, outlet bore and heater bore means. The tubes together with the inlet and outlet boers define a length sufficient to provide a resistance path which minimizes leakage current flow from an electric heater disposed within the heater bore means. A flow responsive switch means controls current flow the electric heater. A thermostat may be provided in series with the flow responsive switch.

23 Claims, 6 Drawing Figures PATEMEU [15825 29/5 SHEET 1 BF 3 TAP PATENTEDuzczs 1915 I 3,78 1.520

sum 3 OF 3 2 1,. 203 ll fi; 262 202 pm PHEA 6M 1 ELECTRIC INSTANTANEOUS WATER HEATER BACKGROUND OF THE INVENTION provided with water inlet and outlet bores connected to a water inlet and a water outlet, wherein the inlet and outlet bores are connected to said heater bore or bores to permit water to flow through said heater bore or bores in contact with the element or elements.

In, for example, the heater which we manufacture and sell under our Trade Mark Alflow, the body is provided with a labyrinth of bores comprising an inlet portion, an outlet portion and a central portion in which the heating elements are disposed, said bores together constituting a flow duct from the water inlet to the water outlet within the body.

Such labyrinths are costly to produce, and, while under most circumstances the labyrinths provide for sufficient electrical resistance in the paths between the inlet and outlet and the elements, when the water supply has a high mineral content, the increased electrical conductivity thereof can reduce the resistance below the level which we desire.

One method of overcoming the problem of sufficient electrical resistance is to increase the size of the body to take further bores to extend the inlet and outlet portions of the labyrinth, but this would increase the cost, size and complexity of the heater, and an object of the invention is to provide a more utilitarian and economical solution to the problem.

SUMMARY OF THE INVENTION Therefore, according to a first feature of the present invention, the body of the heater is constructed so that the heater bores and the inlet and outlet bores are connected to ports, and external tubes of the desired length are connected to the ports to complete a flow duct from the inlet to the outlet of said body via said bores, such that the flow duct provides sufficiently long resistance paths. The tubes are preferably flexible so that they can be accommodated easily in a confined space by being bent or looped.

Preferably, at least that tube carrying hot water from the heater bores to the outlet bore is of temperature stable material of a type suitable for carrying not water, but both or all the tubes may be of similar but differently coloured material to simplify production.

The body may comprise a clamped on portion or cross-member, into which the ends of the tubes may be secured e.g. during moulding thereof.

it has further been found that, by means of the invention, body of the heater may be simplified to a considerable extent by providing such external tubes of a sufficient length, to the extent wherein the body provides merely those bores required for the heater element or elements, for connecting the inlet to one of said ports and the outlet to another of said ports, and for taking water from these said ports to means for controlling the electrical heating current, and thereby the production of the body may be greatly simplified. For example, in the heater which we at present manufacture there are some fourteen upright bores, six longitudinal bores and seven transverse bores in the labyrinth (excluding bores to said controlling devices) disposed in several planes, and this number may be reduced to four axially co-planar upright bores with respective transverse bores to the ports. This enables the body of the heater of the invention to be made by moulding, whereas the prior body has to be made by machining from a solid block and stopping the unwanted drill access holes. Furthermore, this may be achieved without materially altering the existing heaters casing, fittings, back plate,

or controlling devices, and a simplified base plate may be used.

: Furthermore, vin this aforesaid heater which we at present manufacture there are several further ducts and bores to permit water to flow to or through several devices for controlling the electrical heating current and the rate of water flow. Such devices are, to some extent, required because of the nature of the labyrinth in the body and the high cost thereof, and, to some further extent due to the nature of the devices themselves. For example, a pressure sensitive device is provided to switch on the heating current when the water pressure is high enough for the heater to operate. This device includes a diaphragm with a metal backing dish of robust form which operates a switch, and, due to the relatively insensitive nature of the device, the device has to be connected to the inlet bore so that the whole of the back pressure generated by the labyrinth to the flow of water therethrough is available to actuate the device. Of course, if the labyrinth becomes blocked the heating element would burn out if a thermostat device were not provided, and, therefore, such a device is connected by further bores to the heater bores to safeguard the expensive body. The provision of these devices and adapting the body to receive the necessary seals and mounting devices thereof, further increases the already high cost of the known body.

However, further cost savings may be made by taking advantage of the simplified form of body of the present invention, in combination with a preferred further feature of the invention.

According to this preferred feature of the invention the heater has means, for automatically controlling the heating current, comprising a single pressure sensitive switch device having a sensitive resilient diaphragm arrangement which is exposed to water pressure via a duct leading preferably, for example, to the heater bore.

This feature further simplifies the body, to the extent where it is inexpensive enough to be considered to be an expendable item, and since the heater cannot be switched on until there is a sufficient water pressure in the heater bores, the possibility of the heater element burning out is made extremely unlikely and the need for a thermostat is removed.

The pressure sensitive switch device is preferably formed, according to another feature of the invention, so that the working stroke of the diaphragm is sufficiently large that the on and off switch positions lie well within said working stroke, whereby to remove the need for the hitherto usual initial switch setting up and adjusting proceedures. To this end the diaphragm is preferably formed with an annular corrugation, so that a flanged head of a piston may nestle against a central portion of the diaphragm and be surrounded by said corrugation. The head and the diaphragm are preferably located by a cap member which provides an annular abutment for the flange of the head and the peripheral portions of the diaphragm. A switch having an operatdevice.

ing plunger is preferably clamped onto said cap memberso that the plunger extends into the piston. A spring is preferably located about the plunger within'the piston. The diaphragm is preferably provided with a peripheral lip'which sockets into an annular recess provided by the cap member.

In an alternative embodiment the diaphragm arrangement further comprises a supplementary dia phragm which is tied to the aforesaid or main diaphragm by a link, each diaphragm being exposed to the water pressure in a respective part of the flow passage, 50- as to work in opposition and be responsive to the pressure drop causedby a flow of water through the heater to switch on the heating current when a predetermined minimum flow is achieved. This adaptation permits the heater to be incorporated into a water supply system before the water tap, as the heater will switch off when the tap is turned off.

BRIEF DESCRIPTION OF DRAWINGS The invention will now be describedd in further detail, by way of example, with reference to the accompanying drawings which show an embodiment of the heater of the invention, and wherein:

FIG. l shows the body and associated parts of the heater, in front elevation, as installed upon a mounting plate; a

FIG. 2 shows the body in rear elevation;

FIG. 3 shows a partial cross section of said body and parts corresponding to the'line III-III in FIG. 2, showing also afirst embodiment of pressure sensitive switch device; I

FIG. 4 is an enlarged transverse section showing a detail of the end of one of the tubes shown in FIG. 2;

FIG. 5 is apartial vertical cross section showing a second embodiment of the pressure sensitive switch device; and

FIG. 6, is a further partial vertical cross section showing a third embodiment of the pressure sensitive switch DESCRIPTION OF SPECIFIC EMBODIMENTS Asshown in the drawings the heater has a body, of Perspex (a Trade Mark) or a like electrically insulating material, which comprises a main portion and a cross member or portion 1 1. Current control means 12 is secured to the side of the main portion 10 remote from the cross-portion l1, and a'metal bass plate 13, superimposed by a rubber gasket 14, is secured at the bottom of the main portion 10. l

A plastics mounting plate 15 and locator block 16 are provided to carry the body 10, 11 an on/off indicator light.17, a electrical supply cable support 18 and an earth terminal bar 19.

The main portion 10 is provided with an inlet bore 20 having an enlarged threaded lower end in which a metal inlet member 21 is secured through the base plate 13. The upper end of the inlet bores terminates at a port in register with a matching port in thecrossportion 11, said ports being sealed together by a ring seal 22. Said matching port opens into a stepped socket 23 in which one end of a flexible tube 24 is held by means of a ring seal strip 25 and a clamp plate 26.

This tube 24' leads to a similar socket 27 and is secured therein by said ring seal strip 25 and said ,plate' 26. As shown in FIG. 3, a metal liner 28 is provided in the tube ends, which figure also shows the port 29 of said socket 27 sealed'by ring seal 30 to a port 31 of a first heater bore 32 which contains one coil of a heater element 33. The upper end of the coil is connected to a. sealed terminal 34 extending upwardly out of the body, and the lower end is connected through a cross bore 35 to the other coil of said element 33 disposed in a second heater bore 36. The upper end of bore 36 lead through matched registering sealed ports to socket 37. The upper end of the other coil of the element33 is connected to terminal 38. A second tube 39 of nylon material connects the socket 37 with a similar socket 40 which is connected via ports to the upper end of an outlet bore 43 having an enlarged threaded lower end into which an outlet member 44 is secured. The outlet member 44 has a small blow-off port .45 which is nor mally closed by a plastics coverring 46..As is evident, the insulating flexible tubes 24 and 39 are formed separately and independently with respect to the main portion.10 and with respect to each other.

In an unclamped condition as shown in FIGS. 3 and 4,'the-ends of the tubes 24 and 39, each internally supported by the respective liner 28, are located through respective apertures in the ring seal strip 25 and plate 26. The ring seal strip 25 is shaped to provide tubular extensions 41 which extend into recesses provided in the plate 26. When clamping bolts 42 are tightened, the plate 26 is drawn towards the cross-portion 11 thereby compressing the extensions 41 to form tight compression seals about the tube ends, which tube ends are forced some small distance into the stepped sockets 22, 27, 37 and 40, this clamped condition, is shown in FIG.

The first embodiment of heating current control means 12, as shown in FIGS. 2 and 3 is in the form of a switch device responsive to water pressure in heater bore 36,and comprises a diaphragm 50, a piston 51, a cap member 52, a switch 53 and a switch holder 54.

The diaphragm 50 has an annular corrugation 55 about a central portion thereof which is abutted by a flanged head 56 of the piston 51, and a peripheral lip 57 which is located in an annular recess provided in the cap member 52. The cap member 52 is also shaped to provide an annular abutment '58 for the head 56 and corrugation 55.'A spring 59 is located within the hollow piston 51 about an operating plunger 60 of the switch 53. Through bolts 61 are used to clamp the switch holder 54, cap member 52 and body 10 together so that the central portion of the diaphragm 50 overlies a port 62 in the body 10 leading to the heater bore 36. A screw 63 ensures that the switch is securely held in position, and the dimensions of the cap member 52 and outer part of the diaphragm 50 are such as to ensure that the outer part forms a seal against the body 10.

In the second embodiment of heating current control means 12 shown in FIG. 5 there are two diaphragms, namely a main diaphragm 50 and a supplementary diaphragm in the switch device which is responsive to the pressure differential between the inlet bore 20 and the outlet bore 43. The main diaphragm 50 is similar to thediaphragm shown in FIG. 3, as are the parts 51 to 61, except in that the head 56 has a screw extension 156 which passes through the center of the main diaphragm 50 into a tie bar 163. The supplementary diaphragm 150 and its cap member 152 are similar to the diaphragm 50 and cap member 52, a screw and washer assembly 164 being'used to secure the diaphragm 150 to the other end of the tie bar 163. a

The body 110 is identical to the body 10, 11 shown in FIGS. 1 to 4, except in that the port 62 is omitted and instead a port 162 extends from the inlet bore 20 to the front face of the body adjacent the diaphragm 50 and a port 165 extends from the outlet bore 43 to the rear face of the body adjacent the diaphragm 150, and except in that a cross bore is provided in the body to receive, slidably, the bar 163.

The only other exception is that the blow-off port-45 is omitted in this embodiment.

Referring again to FIG. 1, the body 10, 11 or 110, 11 is merely secured upon the mounting plate by means of two bolts 70 and a connection 71 between the base plate 13 and the earth terminal bar 19, so that the inlet and outlet members repose in recesses provided in the locator block 16 and are electrically connected to earth as a safety precaution.

Two of the four bolts 72 used to clamp the body portions 10 or 110 and 11 together serve as terminals 76 and 77 to which the live and neutral wires 73 and 74,

respectively of a mains electrical supply lead 75 can be connected. The internal wiring of the heater is such that the live terminal 76 is connected via the normally open switch 53 to the heater terminal 38 and the heater terminal 34 is connected to the neutral terminal 77, the indicator light 17 being connected in parallel with the heater element 33 via terminals 38 and 34. An earth terminal 78 is provided on the bar 19 to receive the earth wire 79 of the lead 75.

A cover 80, part of which is shown, is provided to enclose the internal parts of the heater, and a cover locating screw socket 81 is provided in the bracket 82 of the indicator light 17.

In use, a main electrical lead 75 is connected as aforesaid and pipework comprising water supply pipe 83 and a discharge pipe 84 are connected to the inlet and outlet members 21 and 44, respectively. In the case of the embodiment of FIGS. 2 to 4 a control tap 85 is connected into the supply pipe 83, and when turned on, the water pressure closes switch 53. In the embodiment of FIG. 5, the tap 85 may alternatively be connected into the discharge pipe 84, and when turned on, the flow of water causes the pressure drop across the heater which closes switch 53.

An automatic non-return valve may be incorporated, for example, into the tap 85, or into the heater.

In the modified embodiment shown in FIG. 6, the internal wiring is such that the live lead 73 is connected via a normally closed thermostat controlled switch 353 and a normally open pressure controlled switch 53 of the automatic control means.

The plunger 60 of switch 53 is actuated by a diaphragm 250 via an adjuster 201, which is required because the diaphragm has a metal backing disk 202 which snaps from the concave normal condition to a convex operative condition when the diaphragm 250 is exposed to sufficient water pressure through a port 262 leading to the inlet bore 20, the screw 203 of the adjuster being pre-set to ensure that the switch operates within the working stroke of the disk.

The switch 353 has a similar adjuster 301 because the diaphragm 350 has a bimetal disk 302 which snaps from its normal condition to the outwardly convex actuating condition when the diaphragm 350is subjected to an excessive temperature. The diaphragm 350 is subjccted to the flow of hot water through ports 361, 362

whichinterrupt the outlet bore 43. In this embodiment the cap member 52 is replaced by a clamp plate 252 which clamps both diaphragms to the main portion 210 of the body, and the switches are located thereon by means of a bracket 254.

A variable flow restrictor 204 is provided so as to intersect the flow duct, whereby to permit the resistance to flow of water through the body to be varied, to vary the flow and therefore the discharge temperature of the water.

It should be noted, that, due to the great electrical resistance provided by the tubes, it is no longer necessary for a central tapping to be provided on the element for connection to the live side of the mains electricity supply.

The invention is not confined to the precise details of the foregoing example, and many variations are possible within its scope. For instance, the number of elements and heater bores may be varied as desired, as may be the configuration of the bores in the body. The body may comprise several clamped together or otherwise secured sections or portions e.g. an inlet section, an outlet section and a heater section whose bores are connected together by said tubes. The body may have further bores to provide labyrinth portions in addition to the tubes to further increase the electrical resistance.

The ends of the tubes may be molded into the sockets during molding of the cross portion or member, or alternatively could be molded into the ports of the main portion or portions during molding thereof, thereby dispensing with the seals and the clamp plate.

A thermostat may, of course, be optionally provided for all embodiments, even though the invention enables such a device to be omitted.

I claim:

1. An instantaneous water heater comprising:

a. a main rigid insulating body having an inlet and an outlet,

b. a flow duct means extending between the inlet and outlet and including an inlet bore, an outlet bore, a heater bore means, first insulating flexible tube means extending between the inlet bore and the heater bore means and a second insulating flexible tube means extending between the heater bore means and the outlet bore,

c. said inlet bore, said outlet bore, and heater bore means being disposed within said main insulating body,

d. electrical heating means disposed in the heater bore means,

e. said tube means together with the inlet bore and outlet bore defining a length sufficient to provide a resistance path which minimizes current flow from the electrical heating means to said inlet and said outlet, and

f. a clamped on portion including a rigid insulating cross member secured to one end of said insulating body,

g. said clamped on portion being removably attached to the insulating body with the ends of the tube means being secured to said clamped on portion,

h. said clamped on portion including first registering port means connecting one end of said inlet bore with one end of said first flexible tube, a second registering port means connecting one end of said heater bore means with the other end of said first flexible tube, third registering port means connecting the other end of said heater bore means with one end of the second flexible tube and fourth registering port means connecting one end of said outlet bore with the other end of said second flexible tube.

2. An instantaneous waterheater comprising:

a. a main rigid insulating body having an inlet and outlet,

b. a flow duct means extending between the inlet and outlet and including an inlet bore, an outlet bore, a heater bore means, first insulating tube means extending between the inlet bore and the heater bore means and second insulating tube means extending between the heater bore means and the outlet bore,

0. said inlet bore, outlet bore, and heater bore means being disposed within said main insulating body,

d. said first and second tube means being formed separately and independently with respect to the main body and with respect to each other,

e. electrical heating means disposed in the heater bore means,

f. said tube 'means together with the inlet bore and outlet bore defining a length sufficient to provide a resistance path which minimizes current flow from the electrical heating means to said inlet and said outlet, and

g. means for connecting said first and second tube means externally with respect to the main insulating body,

h. said connecting means including a rigid insulating cross member secured to one end of the insulating body and a clamping plate mounted for sealing engagement with respect to the cross member,

. said cross member including port means registered with the inlet and outlet bores to allow fluid flow through said flow duct means,

j. said clamping plate including openings to receive the ends of the tube means and register said ends with openings located in the cross member and communicating with the port means.

3. A heater as defined in claim 2 wherein said connecting means includes a sealing strip disposed between the cross member and clamping plate.

4. An instantaneous waterheater comprising:

a. a main rigid insulating body having an inlet bore,

an outlet bore and a heater bore means, an

b. a pipe inlet union rigidly secured in said inlet bore of said body,

c. a pipe outlet union rigidly secured in said outlet bore,

d. heater element means disposed in the heater bore means, 7.

e. a rigid insulating cross member secured to one end portion of said main body,

f. a first insulating flexible tube external of the main body and connected by its ends into said cross member, and

g. a second insulating flexible tube external of .the main body and connected by its ends into said cross member,

h. said main body and said cross member porviding first registering port means connecting one end of said inlet bore with one end of said first tube, second registering port means connecting one end of said heater bore means with the other end of said first tube, third registering port means connecting the other end of said heater bore means with one end of said second tube, and fourth registering connecting one end of said outlet bore with the other end of said second flexible tube,

. the length of the flexible tubes and said inlet and outlet bores being sufiicient to provide a minimum resistance path which minimizes current flow from the heater element means to said inlet and outlet unions.

5. A heater as defined in claim 4 wherein .said rigid inlet and outlet unions secure a metallic base plate against one end of the insulating body, and

grounding means for said heater is electrically connected to the base plate.

6. A heater as defined in claim 4 wherein an automatic control means is attached to the insulating body and is responsive to a change in pressure within said bore means for controlling the electric heating current to said electrical heating means.

7. A heater as defined in claim 6 wherein said control means includes a diaphragm clamped to one side of said body, a duct extending through the wall of said body between said diaphragm and one of said inlet and outlet bores or heater bore means, and an electrical switch secured to said body and actuatable by said diaphragm.

8. A heater as defined in claim 6 wherein said automatic control means includes a non-return valve which controls the flow of water through said flow. duct means. 1

9. A heater as defined in claim 6 wherein said automatic control means includes a pressure sensitive switch and a thermostat wired in series to control the electric heating means.

10. A heater as defined in claim 6 wherein said automatic control means includes a duct extending through the wall of said body, an electrical switch, a movably mounted, spring biased piston member which actuates said electrical switch, a sensitive resilient diaphragm exposed on one side to pressure within said heater bore means via said duct,

said piston member being responsive to movement of said diaphragm, and

the on and of! positions of the electrical switch lie within the working stroke of the diaphragm.

11. A heater as defined in claim 6 wherein said automatic control means includes a single pressure sensitive switch responsive. to pressure in said flow duct means.

12. A heater as defined in claim 11 wherein said pressure sensitive switch includes a resilient diaphragm, a piston means and an electrical switch member,

said control means includes a duct extending through the body between said diaphragm and one of said inlet and outlet bores or said heater bore means,

said diaphragm is exposed on one side to pressure by way of said duct and the piston means is located on the other side of the diaphragm,

said piston means actuates the electrical switch member in response to movement of the resilient diaphragm,

said piston means being spring biased toward said resilient diaphragm.

13. A heater as defined in claim 12 wherein said resilient diaphragm includes an annular corregation and i said piston member has a flanged head which nestles within said annular corrugation.

14. A heater as defined in claim 12 wherein said resilient diaphragm has a flanged rim and said control means includes a cap member which contacts said flanged rim and sealingly engages said insulating body.

15. An instantaneous water heater comprising:

a. a main rigid insulating body having an inlet and an outlet,

b. flow duct means extending between the inlet and the outlet and including an inlet bore, an outlet bore, a heater bore means, first insulating flexible tube means extending between the inlet bore and the heater bore means, and second insulating flexible tube means extending between the heater bore means and the outlet bore,

0. said inlet bore, outlet bore and heater bore means being disposed within said main insulating body, d. said first and second tube means being formed separately and independently with respect to the main bodyand with respect to each other,

e. electrical heating means disposed in the heater bore means,

f. said tube means together with the inlet bore and one end of said insulating body and forming port means therewith to allow fluid flow through said flow duct means,

h. means for securing the ends of said tube means to said port means.

16. An instantaneous water heater comprising:

a. a main rigid insulating body having an inlet and an outlet,

b. flow duct means extending between the inlet and the outlet and including an inlet bore, an outlet bore, a heater bore means, first insulating flexible tube means extending between the inlet bore and heater bore means, and second insulating flexible tube means extending between the heater bore means and the outlet bore,

0. said inlet bore, outlet bore and heater bore means being disposed within said main insulating body, d, said first and second tube means being formed separately and independently with respect to the main body and with respect to each other,

e. electrical heating means disposed in the heater bore means,

f. said tube means together with the inlet bore and outlet bore defining a length sufficient to provide a resistance path which minimizes current flow from the electrical heating means to said inlet and said outlet,

g. a clamped on portion being removably secured to one end of said insulating body and forming port means therewith to allow fluid flow through said flow duct means,

h. means for securing the ends of said tube means to the clamped on portion, and

i. automatic control means attached to the insulating body for controlling the electrical heating current to said electrical heating means in response to the fluid flow through said flow duct means.

17. An instantaneous water heater as defined in claim 16 wherein said automatic control means includes a diaphragm disposed on one side of said body, a duct extending through the wall of said body between said diaphragm and one of the inlet and outlet bores or heater bore means and an electrical switch secured to said main body and actuatable by said diaphragm.

18. A heater as defined in claim 16 wherein said control means includes first and second resilient diaphragm members, first and second ducts extending through the wall of said body, and an electrical switch secured to said body,

said first duct extending between the inlet bore and the first diaphragm member which is thereby exposed on one side to pressure within the inlet bore,

said second duct extending between the outlet bore and the second diaphragm member which is thereby exposed to pressure with the outlet bore, and

said first and second diaphragm members being mechanically tied together,

whereby the control means is responsive to the pressure differential between the inlet and outlet bores.

19. A heater as defined in claim 18 wherein said electrical switch has an off and on position which lies within the working stroke of said first and second diaphragms.

20. A heater member as defined in claim 18 wherein each diaphragm has a flanged rim and a first cap member contacts the flanged rim of said first diaphragm and sealingly engages a first side of the insulating body and a second cap member contacts the flanged rim of said second diaphragm and sealingly engages the other side of the insulating body.

21. A heater member as defined in claim 18 wherein the first and second diaphragm members are located on the same side of the insulating body.

22. An instantaneous water heater having an inlet and an outlet and comprising:

a. an insulating body having a clamped on portion and a main portion, said main portion defining an inlet bore connected to said inlet, an outlet bore connected to said outlet and a heater bore means,

b. an electrical heating means disposed in said heater bore means,

c. said inlet bore, outlet and heater bore means being connected to ports in said clamped on portion to which external tube means are secured whereby to connect said heater bore means to said inlet and outlet bores to form a flow duct means running from said inlet to said outlet,

(1. said tube means being composed of flexible, electrical insulating material, and

e. housing means defining a confined space around the insulating body,

f. said external tubes being looped into the confined space to provide a length of flexible tube means together with the inlet bore or the outlet bore sufficient to form the required long electrical resistance paths between the heating element means and the inlet and outlet.

23. An instantaneous water heater having an inlet and an outlet and comprising:

a. a back plate,

b. a main insulating body secured to said back plate,

c. a cover secured to said back plate to enclose said body,

d. a flow duct means extending between the inlet and outlet and including an inlet bore, an outlet bore,

a heater bore means, first insulating flexible tube means extending between the inlet bore and the heater bore means, and second insulating flexible tube means extending between the heater bore means and the outlet bore, e. said inlet bore, outlet bore, and heater bore means being disposed within said main insulating body, said first and second tube means being formed separately and independently with respect to the main body and-with respect to each other,

g. electrical heating means disposed in the heater bore means,

h. said tube means together with the inlet bore and the outlet bore defining a length sufficient to provide a resistance path which minimizes current means 

1. An instantaneous water heater comprising: a. a main rigid insulating body having an inlet and an outlet, b. a flow duct means extending between the inlet and outlet and including an inlet bore, an outlet bore, a heater bore means, first insulating flexible tube means extending between the inlet bore and the heater bore means and a second insulating flexible tube means extending between the heater bore means and the outlet bore, c. said inlet bore, said outlet bore, and heater bore means being disposed within said main insulating body, d. electrical heating means disposed in the heater bore means, e. said tube means together with the inlet bore and outlet bore defining a length sufficient to provide a resistance path which minimizes current flow from the electrical heating means to said inlet and said outlet, and f. a clamped on portion including a rigid insulating cross member secured to one end of said insulating body, g. said clamped on portion being removably attached to the insulating body with the ends of the tube means being secured to said clamped on portion, h. said clamped on portion including first registering port means connecting one end of said inlet bore with one end of said first flexible tube, a second registering port means connecting one end of said heater bore means with the other end of said first flexible tube, third registering port means connecting the other end of said heater bore means with one end of the second flexible tube and fourth registering port means connecting one end of said outlet bore with the other end of said second flexible tube.
 2. An instantaneous water heater comprising: a. a main rigid insulating body having an inlet and outlet, b. a flow duct means extending between the inlet and outlet and including an inlet bore, an outlet bore, a heater bore means, first insulating tube means extending between the inlet bore and the heater bore means and second insulating tube means extending between the heater bore means and the outlet bore, c. said inlet bore, outlet bore, and heater bore means being disposed within said main insulating body, d. said first and second tube means being formed separately and independently with respect to the main body and with respect to each other, e. electrical heating means disposed in the heater bore means, f. said tube means together with the inlet bore and outlet bore defining a length sufficient to provide a resistance path which minimizes current flow from the electrical heating means to said inlet and said outlet, and g. means for connecting said first and second tube means externally with respect to the main insulating body, h. said connecting means including a rigid insulating cross member secured to one end of the insulating body and a clamping plate mounted for sealing engagement with respect to the cross member, i. said cross member including port means registered with the inlet and outlet bores to allow fluid flow through said flow duct means, j. said clamping plate including openings to receive the ends of the tube means and register said ends with openings located in the cross member and communicating with the port means.
 3. A heater as defined in claim 2 wherein said connecting means includes a sealing strip Disposed between the cross member and clamping plate.
 4. An instantaneous water heater comprising: a. a main rigid insulating body having an inlet bore, an outlet bore and a heater bore means, an b. a pipe inlet union rigidly secured in said inlet bore of said body, c. a pipe outlet union rigidly secured in said outlet bore, d. heater element means disposed in the heater bore means, e. a rigid insulating cross member secured to one end portion of said main body, f. a first insulating flexible tube external of the main body and connected by its ends into said cross member, and g. a second insulating flexible tube external of the main body and connected by its ends into said cross member, h. said main body and said cross member porviding first registering port means connecting one end of said inlet bore with one end of said first tube, second registering port means connecting one end of said heater bore means with the other end of said first tube, third registering port means connecting the other end of said heater bore means with one end of said second tube, and fourth registering connecting one end of said outlet bore with the other end of said second flexible tube, i. the length of the flexible tubes and said inlet and outlet bores being sufficient to provide a minimum resistance path which minimizes current flow from the heater element means to said inlet and outlet unions.
 5. A heater as defined in claim 4 wherein said rigid inlet and outlet unions secure a metallic base plate against one end of the insulating body, and grounding means for said heater is electrically connected to the base plate.
 6. A heater as defined in claim 4 wherein an automatic control means is attached to the insulating body and is responsive to a change in pressure within said bore means for controlling the electric heating current to said electrical heating means.
 7. A heater as defined in claim 6 wherein said control means includes a diaphragm clamped to one side of said body, a duct extending through the wall of said body between said diaphragm and one of said inlet and outlet bores or heater bore means, and an electrical switch secured to said body and actuatable by said diaphragm.
 8. A heater as defined in claim 6 wherein said automatic control means includes a non-return valve which controls the flow of water through said flow duct means.
 9. A heater as defined in claim 6 wherein said automatic control means includes a pressure sensitive switch and a thermostat wired in series to control the electric heating means.
 10. A heater as defined in claim 6 wherein said automatic control means includes a duct extending through the wall of said body, an electrical switch, a movably mounted, spring biased piston member which actuates said electrical switch, a sensitive resilient diaphragm exposed on one side to pressure within said heater bore means via said duct, said piston member being responsive to movement of said diaphragm, and the on and off positions of the electrical switch lie within the working stroke of the diaphragm.
 11. A heater as defined in claim 6 wherein said automatic control means includes a single pressure sensitive switch responsive to pressure in said flow duct means.
 12. A heater as defined in claim 11 wherein said pressure sensitive switch includes a resilient diaphragm, a piston means and an electrical switch member, said control means includes a duct extending through the body between said diaphragm and one of said inlet and outlet bores or said heater bore means, said diaphragm is exposed on one side to pressure by way of said duct and the piston means is located on the other side of the diaphragm, said piston means actuates the electrical switch member in response to movement of the resilient diaphragm, said piston means being spring biased toward said resilient diaphragm.
 13. A heater as defined in claim 12 wherEin said resilient diaphragm includes an annular corregation and said piston member has a flanged head which nestles within said annular corrugation.
 14. A heater as defined in claim 12 wherein said resilient diaphragm has a flanged rim and said control means includes a cap member which contacts said flanged rim and sealingly engages said insulating body.
 15. An instantaneous water heater comprising: a. a main rigid insulating body having an inlet and an outlet, b. flow duct means extending between the inlet and the outlet and including an inlet bore, an outlet bore, a heater bore means, first insulating flexible tube means extending between the inlet bore and the heater bore means, and second insulating flexible tube means extending between the heater bore means and the outlet bore, c. said inlet bore, outlet bore and heater bore means being disposed within said main insulating body, d. said first and second tube means being formed separately and independently with respect to the main body and with respect to each other, e. electrical heating means disposed in the heater bore means, f. said tube means together with the inlet bore and outlet bore defining a length sufficient to provide a resistance path which minimizes current flow from the electrical heating means to said inlet and said outlet, g. a clamped on portion being removably secured to one end of said insulating body and forming port means therewith to allow fluid flow through said flow duct means, h. means for securing the ends of said tube means to said port means.
 16. An instantaneous water heater comprising: a. a main rigid insulating body having an inlet and an outlet, b. flow duct means extending between the inlet and the outlet and including an inlet bore, an outlet bore, a heater bore means, first insulating flexible tube means extending between the inlet bore and heater bore means, and second insulating flexible tube means extending between the heater bore means and the outlet bore, c. said inlet bore, outlet bore and heater bore means being disposed within said main insulating body, d. said first and second tube means being formed separately and independently with respect to the main body and with respect to each other, e. electrical heating means disposed in the heater bore means, f. said tube means together with the inlet bore and outlet bore defining a length sufficient to provide a resistance path which minimizes current flow from the electrical heating means to said inlet and said outlet, g. a clamped on portion being removably secured to one end of said insulating body and forming port means therewith to allow fluid flow through said flow duct means, h. means for securing the ends of said tube means to the clamped on portion, and i. automatic control means attached to the insulating body for controlling the electrical heating current to said electrical heating means in response to the fluid flow through said flow duct means.
 17. An instantaneous water heater as defined in claim 16 wherein said automatic control means includes a diaphragm disposed on one side of said body, a duct extending through the wall of said body between said diaphragm and one of the inlet and outlet bores or heater bore means and an electrical switch secured to said main body and actuatable by said diaphragm.
 18. A heater as defined in claim 16 wherein said control means includes first and second resilient diaphragm members, first and second ducts extending through the wall of said body, and an electrical switch secured to said body, said first duct extending between the inlet bore and the first diaphragm member which is thereby exposed on one side to pressure within the inlet bore, said second duct extending between the outlet bore and the second diaphragm member which is thereby exposed to pressure with the outlet bore, and said first and second diaphragm members being mechanically Tied together, whereby the control means is responsive to the pressure differential between the inlet and outlet bores.
 19. A heater as defined in claim 18 wherein said electrical switch has an off and on position which lies within the working stroke of said first and second diaphragms.
 20. A heater member as defined in claim 18 wherein each diaphragm has a flanged rim and a first cap member contacts the flanged rim of said first diaphragm and sealingly engages a first side of the insulating body and a second cap member contacts the flanged rim of said second diaphragm and sealingly engages the other side of the insulating body.
 21. A heater member as defined in claim 18 wherein the first and second diaphragm members are located on the same side of the insulating body.
 22. An instantaneous water heater having an inlet and an outlet and comprising: a. an insulating body having a clamped on portion and a main portion, said main portion defining an inlet bore connected to said inlet, an outlet bore connected to said outlet and a heater bore means, b. an electrical heating means disposed in said heater bore means, c. said inlet bore, outlet and heater bore means being connected to ports in said clamped on portion to which external tube means are secured whereby to connect said heater bore means to said inlet and outlet bores to form a flow duct means running from said inlet to said outlet, d. said tube means being composed of flexible, electrical insulating material, and e. housing means defining a confined space around the insulating body, f. said external tubes being looped into the confined space to provide a length of flexible tube means together with the inlet bore or the outlet bore sufficient to form the required long electrical resistance paths between the heating element means and the inlet and outlet.
 23. An instantaneous water heater having an inlet and an outlet and comprising: a. a back plate, b. a main insulating body secured to said back plate, c. a cover secured to said back plate to enclose said body, d. a flow duct means extending between the inlet and outlet and including an inlet bore, an outlet bore, a heater bore means, first insulating flexible tube means extending between the inlet bore and the heater bore means, and second insulating flexible tube means extending between the heater bore means and the outlet bore, e. said inlet bore, outlet bore, and heater bore means being disposed within said main insulating body, f. said first and second tube means being formed separately and independently with respect to the main body and with respect to each other, g. electrical heating means disposed in the heater bore means, h. said tube means together with the inlet bore and the outlet bore defining a length sufficient to provide a resistance path which minimizes current flow from the electrical heating means to said inlet and said outlet, i. a clamped on portion being removably secured to one end of said insulating body annd forming port means therewith to allow fluid flow through said flow duct means, j. means for securing the ends of said tube means to said port means, and k. switch means mounted on said body to control the flow of electric current to said electrical heating means. 